A common problem throughout many industries is exposure of extremely valuable and costly structures and equipment to corrosive, toxic and/or abrasive elements. For example, the sewer line industry is currently faced with repairing, restoring and/or replacing thousands of miles of public and private sewer lines. The City of Seattle has recently allocated in excess of seventeen million dollars ($17,000,000.00) for the year of 1997 to restore damaged sewer lines within its jurisdiction.
Such damaged sewer lines are primarily manufactured from concrete.
In the case of sewer lines, hydrogen sulfide gasses out above the sewage line of the contained sewage. Hydrogen sulfide is very corrosive. Over a period of time, the hydrogen sulfide eats at and corrodes away the concrete to a point that a maintenance crew must excavate the sewer line, and clean, repair, restore and/or replace it.
As found within sewer lines, many corrosive, toxic and abrasive problems appear to concentrate slightly below and/or above the water line.
Within the marine industry, piers, seawalls, floating bridges, bridge pilings, retaining walls, wave breakers, boats, ships, barges, and related equipment are regularly exposed to tide fluctuations, wave splash, electrochemical disintegration, and a host of other corrosive, toxic and abrasive problems. Again, these problems are located primarily at or above the water line.
The United States government, and particularly the Coast Guard and Navy, are currently faced with a large number of steel seawall structures that require immediate repair. Metal placed below the water line can be easily treated and protected using an electrified cathode. This type of corrosion treatment below the water line is known as cathodic protection. Basically, cathodic protection uses a sacrificial anode or an impress current system to stop rust on an ionic or on a molecular level. Since water is an electrolyte, electrical currents are easily dealt with below the water line. In other words, as long as there is water, the structure below the water line can be very easily protected electrically through use of a cathode.
Significant problems arise, however, within the atmospheric and splash zone area of the structure. It is very difficult to prevent corrosion within the atmospheric and splash zone area of a structure. The causes or effects of atmospheric corrosion are many. For example, a steel structure is exposed to water and air, and continually passes through a wet and dry cycle. In an oceanic or saltwater environment, chloride, chlorine, and/or salt is repeatedly splashed onto the structure. Once salt splashes onto the structure corrosion begins. The old salt is then washed off and fresh salt is splashed onto the structure. This is the common corrosion effect or problem that oceanic structures are continually facing.
In the past, steps were generally taken to protect concrete sewer lines and steel seawall structures against such corrosive, toxic and abrasive forces. For example, over the past fifteen (15) to thirty-five (35) years, many of such structures were coated with coaltar epoxy, polyamide epoxy, or urethane in an effort to stop decay. The nearly universal failure of such coatings has caused the current need to repair these structures.
Another factor that breaks down the heretofore used anti-corrosion protective systems is the effects of ultraviolet (UV) radiation upon the exposed structures and/or protective barriers. Ultraviolet radiation of the sun causes a chemical breakdown and deterioration within the protective barrier.
The cost of repairing damaged surfaces and structures can be extremely high. For example, relining sewer lines with the same antiquated materials and application procedures costs about $30.00 to $35.00 for each square foot of repair. The repair is accomplished by excavating the broken or corroded sewer line, trowel applying a tar mastic to the damaged section of line, and then hand applying and wrapping a liner around the sewer line over the tar mastic.
The cost to repair damaged seawall structures within the marine industry, using similar antiquated materials and application procedures, is currently about $30.00 for each square foot of repair.
Such repair procedures require the implementation of a large number of highly labor-intensive steps or procedures in order to get the tar mastic to stick or adhere to the sewer lines or other substrate surface.
Please keep in mind that the sewer line or other failing substrate structure has been exposed to corrosive, toxic and/or abrasive elements for years, if not decades, of use. As a consequence, the substrate structure itself is usually failing or decomposing. In addition, there may be a substantial amount of debris, such as soil, dirt, mud, clay, gravel, sewage, grime, salt, organic material, radioactive material, old coatings, and the like, that are still clinging to the sides of the substrate.
In order to properly prepare the substrate surface, the substrate must be: excavated; brushed, swept or chemically scoured; and subjected to one or more jets of pressurized air and/or water, or abrasive media at very elevated pressures. The substrate must then be allowed to dry before the tar mastic is applied.
For the tar mastic to provide any protection whatsoever, it must be applied with a substantial thickness and be relatively stable after it is applied. In other words, if the tar mastic is too thin, it will be easily applied. However, thin applications of tar mastic will not be sufficiently thick to provide the desired protection. Furthermore, thin coats of tar mastic may run off of the surface being coated, thereby thwarting repair efforts.
Conversely, if the tar mastic is too thick, it is very difficult to apply and use. Thick coats of applied tar mastic do not adhere well to the substrate, which again thwarts the purpose of the repair.
In order to obtain an acceptable compromise between these two extreme conditions, solvents are usually stirred or mixed into the tar mastic. The solvent makes the tar mastic thinner, more viscous, and easier to trowel or hand apply. For example, a toluene solvent of about fifty percent (50%) by volume may be mixed into a polyisobutylene-type of mastic.
In other words, a thick tar mastic can be thinned down using a solvent that over time will evaporate out. The thinner liquid is then coated onto the substrate surface. If the tar mastic is thinned down sufficiently, it may permeate into the surface of the substrate. The solvent then evaporates out and leaves a more solidified mastic behind.
Once applied, the thinned-out, solvent-laden tar mastic must be allowed to cure. In essence the solvent is permitted to evaporate out into the atmosphere, leaving behind a more viscous, slightly tougher tar mastic on the substrate surface. The solvent is intended to carry the tar mastic into the pores of the substrate surface. The solvent then evaporates out, leaving the tar mastic on the surface.
This curing procedure requires a significant amount of time. During the curing time, the work crew cannot perform any other functions at that location, and the structure cannot be used. Such delays can be very costly and expensive. Furthermore, tidal flows and other time sensitive conditions may not permit the use of long curing times.
The above described procedures face another significant problem. Due to public concern over the environment, governmental regulations and laws have become extremely strict. Such regulations and laws often govern how a procedure is to be performed. For example, there are very strict regulations and rules as to what is considered a contaminant. The debris which is scraped, sprayed and washed off of the substrate surface may very well comprise subject contaminants. Furthermore, the solvents used to thin down the tar mastic are also likely subject contaminants. Many of these regulations and laws state basically that no contaminants can enter into the environment. Therefore, it is important to obtain a one-hundred percent (100%) collection rate of all such contaminants. Failure to conform to such regulations and laws can expose the repair company and/or municipality to severe fines and political fallout.
Heretofore, it was very expensive and difficult, if not impossible, to obtain a one-hundred percent (%100) contaminant collection rate when such aforementioned procedures are used on huge seawalls that are located in non-static environments, i.e., within tidal and/or wave zones.
Industries that repair such structures are very much entrenched in the foregoing procedures. The primary reason for this entrenchment is the lack of adequate alternative procedures.
There are unrelated coating systems that are used in very different environments than those discussed above. For example, clean metals such as aluminum can be anodized. However, even if it could be done, no one in their right mind would want to anodize a contaminated, corroded concrete sewer line. Similarly, by investing great expense, exercising rigorous and time consuming metal preparation procedures, and placing the metal within a controlled environment, such metal can be thoroughly cleaned. The status quo within current coating technology is that the substrate must be completely clean. In order to provide long-term performance, the substrate surface or profile is mechanically sandblasted to remove all contamination therefrom.
Once properly cleaned, the metal can then be heated to elevated temperatures and a spray of molten thermoplastic may be directed toward the hot metal to place a coat of thermoplastic thereupon. However, unless the metal is extremely clean and the proper temperatures maintained throughout the process, the thermoplastic will not adhere to the metal and will simply peel off. Due to the difficulties associated with applying this form of coating, such coating systems necessarily have very limited warranties. Furthermore, such coating systems have a very small range of application.
The inventor believes that the above-listed information, whether taken alone or in combination, neither anticipate nor render obvious the present invention. The foregoing explanation does not constitute an admission that such information is relevant or material to the claims of this patent document.